Recursion in SQL - | Stanford Lagunita · Jennifer Widom Linear Recursion With Recursive R As (base...
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Jennifer Widom Recursion in SQL Nonlinear and Mutual Recursion
Transcript of Recursion in SQL - | Stanford Lagunita · Jennifer Widom Linear Recursion With Recursive R As (base...
Jennifer Widom
Recursion in SQL
Nonlinear and Mutual Recursion
Jennifer Widom
SQL With Recursive Statement
With Recursive R1 As (query-1), R2 As (query-2), ... Rn As (query-n)
<query involving R1,…,Rn (and other tables)>
Nonlinear & Mutual Recursion
Jennifer Widom
SQL With Recursive Statement
With Recursive R As ( base query Union recursive query )
<query involving R (and other tables)>
Nonlinear & Mutual Recursion
Jennifer Widom
Linear Recursion
With Recursive R As ( base query Union recursive query )
<query involving R (and other tables)>
Nonlinear & Mutual Recursion
Jennifer Widom
Example: Ancestors
ParentOf(parent,child) Find all of Mary’s ancestors
Nonlinear & Mutual Recursion
Jennifer Widom
Example: Ancestors
ParentOf(parent,child) Find all of Mary’s ancestors
Nonlinear & Mutual Recursion
Jennifer Widom
Example: Ancestors
ParentOf(parent,child) Find all of Mary’s ancestors
Nonlinear (versus linear) + Query looks cleaner
+ Converges faster
– Harder to implement
SQL standard only requires linear
Nonlinear & Mutual Recursion
Jennifer Widom
SQL With Recursive Statement
With Recursive R1 As (query-1), R2 As (query-2), ... Rn As (query-n)
<query involving R1,…,Rn (and other tables)>
Nonlinear & Mutual Recursion
Jennifer Widom
Mutual Recursion
With Recursive R1 As (query-1), R2 As (query-2), ... Rn As (query-n)
<query involving R1,…,Rn (and other tables)>
Nonlinear & Mutual Recursion
Jennifer Widom
Example: Hubs & Authorities
Link(src,dest)
HubStart(node) AuthStart(node)
Nonlinear & Mutual Recursion
Jennifer Widom
Example: Hubs & Authorities
Link(src,dest)
HubStart(node) AuthStart(node)
Nonlinear & Mutual Recursion
Jennifer Widom
Nonlinear & Mutual Recursion
Example: Hubs & Authorities
Jennifer Widom
Example: Recursion with Aggregation
P(x)
Nonlinear & Mutual Recursion
Jennifer Widom
SQL With Recursive Statement
Extends expressiveness of SQL Basic functionality: linear recursion
Extended functionality: nonlinear recursion, mutual recursion
Disallowed: recursive subqueries (negative), aggregation
With Recursive R1 As (query-1), R2 As (query-2), ... Rn As (query-n)
<query involving R1,…,Rn (and other tables)>
Nonlinear & Mutual Recursion
